try scrolling with pagedown a less viewed file of long lines 
say a line of 72k chars , when about that position in the line, you get to see
the pagedown scroll  going line-by-line

this happens even without less, but in less it can be controlled
and without less, just ie.
grep -r kernel --exclude-dir=.config --exclude-dir=build
in my home folder
(if it gets into ~/.mozilla/firefox/*.default/sessionstore-backups/previous.js for example)

will make urxvt unresponsive with 100% cpu usage
and thus u'd have to either wait or kill it


